Lesson 11- circadian rhythms

Question 1

Circadian rhythms

Answer 1

-24 hour, known as body clock, reset by levels of light, biological representation of 24 hour day, optimises an organisms physiology and behaviour to best meet demands of day/night cycle
-driven by suprachiasmatic nuclei in hypothalamus, pacemaker, must be constantly reset so that our bodies are in synchrony with outside world
-natural light provides input to this system, setting body clock to right time-photoentrainment, in mammals light sensitive cells within the eye act as a brightness detectors, sending messages about the environmental light to the scn, then uses info to coordinate activity of circadian rhythm

Question 2

Sleep wake cycle

Answer 2

-light and dark are external signs determining cycle, rhythm dips and rises at different times of day so that strongest sleep drive occurs at 2-4 am and 1-3pm, sleepiness is less intense with sufficient sleep vice versa
-sleep and wake under homeostatic control, when awake for a long time homeostasis tells us the need for sleep is increasing because of amount of energy used up during,homeostatic drive for sleep increases gradually throughout the day, reaches max in late evening
-circadian system keeps us awake as long as there is daylight, prompts sleep as it becomes dark, homeostatic system makes us sleepier regardless, internal circadian clock will maintain a cycle of 24-25 hours even in absence of external cues as free-running

Question 3

core body temperature

Answer 3

-sleep occurs when core temp begins to drop and begins to rise in last few hours of sleep prompting feeling of alertness in morning
-Folkard et al 1977 demonstrated how children who had stories read to them at 3pm showed superior recall and and comprehension after a week compared to children who heard the same stories at 9am
-Gupta 1991 found improved performance on iq tests when participants were assessed at 7pm as opposed to 2pm and 9pm, small drop in body temp does occur in most people between 2-4pm may explain afternoon sleepiness/findings

Question 4

circadian rhythms evaluation

Answer 4

-chronotherapeutics, time patients take medication very important in treatment success,right concentration to target area when most needed, heart attacks morning prone, research has helped
-better understanding of consequences of disruption of circadian rhythms through desynchonisation eg shift work, reduced period of concentration at 6am, mistakes, reshuffle
also link between shift workers and health, Knutsson 2003 found shift workers are three times more likely to develop heart disease
-uses case studies, small sample sizes, especially sleep/wake cycle, questions generalisability of studies, representative of target population, Michael Siffre 1999 cave experience, observed at the age of 60 his internal clock ticked much more slowly than when he was a young man, illustrates that even when the same person is involved there are varying factors that prevent general conclusions being drawn
-early research studies suffered important flaw when estimating ‘free-running’ cycle of human circadian rhythm, in most studies pps deprived of objects that could affect rhythms such as clocks, daylight, but werent deprived of artificial light
however Czeisler et al 1999 was able to alter pps circadian rhythms to between 22-28 hours by manipulating the use of artificial lighting along, suggests circadian rhythms may not be so timely after all